Conventionally, as the format of the map data for the navigation apparatus, in Japan, for example, KIWI method is generally used. A road on the map is represented by the unit of links in this method, and each link has the reference information of the start point node and the end point node. Further, the map data of the above representation method has a hierarchy of multiple layers for the purpose of speeding-up of the route finding and the like, with link IDs as the identification information assigned to each of the links in the lowest layer.
More specifically, for the purposes of data compression and efficiency of image drawing of the road with the same attributes, the links having the same attributes and being arranged in succession are grouped as a link series. Therefore, the links in the link series have the successive link IDs. In this manner, the link series is represented, in the upper layer, by the link IDs of the start side link and the end side link, for the purpose of identifying each of the links in the link series.
However, the map data in the navigation apparatus must be partially updated due to the change of the actual roads and other causes, thereby posing a problem of consistency maintenance, that is, how to manage the link IDs when existing links are divided/split into two, or two links are merged, for example, with the successive numbering of link IDs kept intact. In other words, the link data update processing requires huge processing load for the maintenance of the successive numbering.
In order to solve the numbering problem, the link numbering scheme that (a) the lowest layer links are respectively assigned with the unique link IDs in a scope of 1000 to 1099, for example, and (b) the links in a single link series has the successive link IDs such as 1000 to 1099 and 1100 to 1199, is proposed in Japanese patent document JP3725022. In the above-described manner, the existing link can be divided, for example, by dividing the above link scope to two scopes of 1000 to 1049 and 1050 to 1099. That is, the link ID successiveness is kept by dividing the scope of link IDs.
However, the update scheme disclosed in the above Japanese patent document JP3725022 that the link renumbering is saved only in a case that the scope of the link IDs covers the post-splitting link IDs, as shown in FIG. 15B. That is, if the scope of the post-splitting link IDs exceeds a predefined link ID scope, the link ID re-numbering is still required, as shown in FIG. 15C. That is, the solution presented in the above patent document is not fundamental. The scope of the link IDs may be enhanced in the above technique, only with the accompanying increase of the data amount. Further, how to define an appropriate scope of the link IDs introduces another complicacy into the data management.